When connecting a trailer to a vehicle, it is often important for different kinds of systems and components in the vehicle to be aware of the trailer in order to ensure proper operation of the vehicle. This is true for such systems as, for example, automatic gear boxes, brake systems and light systems all of which may apply different kinds of automated programs depending on the presence or absence of a trailer.
The detection of the presence or absence of a trailer is of particular importance for trucks, and thus for truck drivers, but can also be important for drivers of ordinary vehicles when attaching trailers, campers, caravans and the like.
Conventionally, detecting the absence or presence of a trailer has been carried out by measuring the current going to the light system of the trailer, a current which is conventionally fed via a power line attached to the vehicle. Since conventional trailers have lamps of the traditional design, the current consumed by the light system of the trailer has typically been quite high. This normally made it easy to detect the presence or absence of a trailer by measuring the current at an outlet of the vehicle to a power line to a trailer, and comparing the level of that current to a known threshold. In addition, since such currents are so high, it has been possible to carry out the measurement by means of components which have rather poor resolution, making the components and also the measurement inexpensive.
Recently, however, vehicles and trailers have begun using lights equipped with Light Emitting Diodes, or LED:s. One property of such diodes is that they consume a minimal amount of power compared to conventional lights. This is advantageous in many ways, but it makes the detection as explained above difficult or impossible since the amount of power consumed by a trailer equipped with LED-lights involves currents which will not be above the threshold for conventional lights, and might not even be at a level which is even theoretically possible to detect with the kinds of components traditionally utilized.
Thus, if a vehicle has a trailer connected and the trailer is equipped with LED lights, the systems in the vehicle which use information regarding the presence or absence of a trailer will receive erroneous information.